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I've been reading about DHCP and see that it uses limited broadcast to send its initial request to reach a DHCP server. I read about limited broadcast too which says it sends the message to every computer in the Local Area Network. A couple of questions I don't think I understand properly:

  1. Does this mean every ordinary computer on the network is receiving this message and just ignoring this? I see a DHCP server listens on port 67 for these requests. Is it the job of a computer's firewall to be filtering out these messages that appear on port 67?

  2. I also read about rogue DHCP servers. These would then be these computers that choose to respond to these messages rather than ignore the message?

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  1. Does this mean every ordinary computer on the network is receiving this message and just ignoring this?

Yes. Most devices do not have a process listening to UDP on port 67 to respond as a DHCP server, so receiving a broadcast on UDP port 67 is ignored, although the host is interrupted to pass it up the network stack and determine that it does not actually have such a process attached to UDP on port 67.

I see a DHCP server listens on port 67 for these requests. Is it the job of a computer's firewall to be filtering out these messages that appear on port 67?

No. With no process attached to UDP on port 67, a host will simply drop the traffic in the network stack because there is not process to handle the traffic. Only IPv4 uses UDP on port 67 as a DHCP server; IPv6 does it differently, using multicast instead of broadcast.

  1. I also read about rogue DHCP servers. These would then be these computers that choose to respond to these messages rather than ignore the message?

Yes. A host with a DHCP server process attached to UDP on port 67 will respond to DHCP messages received. That is a DHCP server, rogue or not.

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